The present invention relates, in general, to the field of hydrodynamic bearings. More particularly, the present invention relates to a hydrodynamic bearing configuration utilizing one or more inverted surface tension seals which is of particular utility in conjunction with the rotating hub and disk stack of a computer mass storage device disk drive. The hydrodynamic bearing of the present invention provides enhanced tilt stiffness during rotation of the disk stack by allowing for an increased distance between the centers of force acting at the upper and lower bearing journals, thereby resulting in an effectively greater spindle length for a given height form factor disk drive.
Disk drives are computer mass storage devices from which data may be read and/or to which such data may be written. In general, they comprise one or more randomly accessible rotating storage media, or disks, on which data is encoded by various means. In magnetic disk drives, data is encoded as bits of information comprising magnetic field reversals grouped in tracks on the magnetically-hard surface of the rotating disks. The disks are stacked in a generally parallel and spaced-apart relationship and affixed at their inner diameter ("ID") to a common hub which is rotationally coupled to a stationary spindle shaft by a pair of bearings, typically ball bearings.
With the growing trend toward even lower height form factor disk drives, the length of the spindle shaft and spacing between the upper and lower bearings becomes a significant consideration in meeting specific drive height constraints. As drive height is decreased, a proportionately shorter spindle must be accommodated within the decreased height constraints with a concomitantly shorter spacing available between the upper and lower bearings supporting the hub on the spindle.
Inasmuch as conventional ball bearings have inherently limited stiffness themselves and exhibit many spring-like properties, shorter spacing between the upper and lower bearings results in reduced tilt stiffness as well as a reduced rocking mode frequency. Given the various excitation frequencies in an operating disk drive, whether due to defects and imperfections in the races and ball bearings or other factors, reduced tilt stiffness and lower rocking mode frequency can cause drive failure if it becomes coincident with these excitation frequencies. In addition, the lubricant film thicknesses associated with ball bearings are very thin, providing little attenuation of surface defects and imperfections in the ball bearings. This results in large amounts of repetitive runout, or repetitive path deviation traced out by the spin axis of the spindle bearing. In addition, ball bearings may exert excessive force on the attached disk drive structure, leading to eventual structural damage.
The aforementioned United States patents describe a hydrodynamic bearing of particular utility in overcoming the inherent disadvantages of conventional ball bearing supported spindles. In particular, the design therein disclosed provides much improved runout characteristics over ball bearing designs due to its use of a relatively thick lubricant film between the sliding metal surfaces which simultaneously provides a high degree of viscous damping to significantly attenuate non-repetitive runout. As a result, increased tracking performance may be achieved allowing for enhanced drive track densities. Moreover, the lubricant film also serves to dampen external shock and vibration resulting in a more robust drive especially desirable in conjunction with portable computer equipment.
Nevertheless, the particular structure of the bearings disclosed in these patents extends the seals axially outward from the center of the bearing, in effect limiting the distance between the centers of force acting at the upper and lower bearing journals as dictated by the particular drive height form factor. The resultantly smaller distance between the centers of force, as with conventional ball bearing designs, limits the overall tilt stiffness of the bearing.
Consequently, a need remains in the art for a hydrodynamic bearing having improved tilt stiffness while retaining the advantages of high precision with low repetitive and non-repetitive runouts associated with conventional hydrodynamic bearing designs.